A Fast and Rigorous 3D Inversion of the Marine CSEM Data

Marine controlled source electromagnetic (MCSEM) surveys have become an important part of the offshore petroleum exploration. However, due to enormous computational difficulties of the full 3-D inversion, the practical interpretation of the MCSEM data is still based on qualitative analysis and relatively simple 2-D geoelectrical models of the sea-bottom structures. In this paper we present a new approach to 3-D inversion of the MCSEM data. It is based on the rigorous integral equation (IE) forward modeling and a new IE representation of the sensitivity (Frechet derivative matrix) of the observed data to the variations of the sea-bottom conductivity. This approach requires just one forward modeling on every iteration of the regularized gradient type inversion algorithm, which speeds up the computations significantly. We also use a regularized focusing inversion method, which provides a sharp boundary image of the petroleum reservoir. The methodology is tested on a 3-D inversion of the synthetic EM data representing a typical MCSEM survey conducted for offshore petroleum exploration.